Keeping it polite...and within the rules of the game...what would you armchair coaches out there recommend as the best defensive strategy to neutralize Tomkins?

I thought you were going to ask for donations to stop him going to RU or the NRL.

Not sure it can be done. (Not keeping it polite and within the rules of the game anyway.)
Some players, on their day, just can't be stopped. Tomkins has more of those days than most.
He is a prodigiously talented player whose only major fault imo is that he doesn't play for the team I support.

At all costs avoid kicking to him, try manipulate kicks to wingers. This guy is utter class though. Absolute hats off to him just seems to get better and better.

Kick more towards the wingers.

Try to maintain a strong defensive line because he's lethal in a broken field.

Just hoof it dead/into touch (make sure it bounces, obviously).

Then when he has the ball in attack, defend him the same way Chase can be defended and get in his face in a group, rough him up a bit.

Dont kick towards the wingers whatever you do. If they get a quick play the ball he will be away and it will be a try or huge gain on play 2. Kick straight to him and keep your line solid. In general play I have no idea how you would stop him.

Sam Tomkins doesn't take the first carry on a kick return as much as he used to do. If he takes the ball he'll usually pass to one of our bigger wingers - Charnley/Richards/Gelling - and they'll drive the ball in hard & look for a quick POTB. Sam will jump into dummy half & look to catch the markers out of position or if the defence has their back turned to him he'll run at you and is very difficult to put down because he accelerates off the mark so quickly and has outstanding footwork and balance. If it doesn't lead to a break/try it will lead to a penalty with the markers not square or the defenders are offside. So on kick chase you have to move up as a unit & have no-one jumping out the line. If he hasn't returned the kick, make sure on play 2 that your markers are set and concentrating otherwise he'll catch you out better than most.

In general play it's a whole difference ball game. You're not stopping Sam Tomkins as such you're stopping the Wigan machine. We have our systems/structures in place where every player has a role in the attack. It's practically two (sometimes three) waves of attack with our forwards running excellent lines (who are all viable options so the defence has to concentrate) and then our backs are the second wave who are all quick and evasive so the defence must make the right decision on whether the ball will stay with Finch/Leuluai/McIlorum or will hit a forward or will come to a back. Then you have Sam Tomkins who roams around in the background & will offer himself as a third option. He attracts defenders so can be used as a dummy runner but more often than not he'll get the ball in the space that the waves of attackers has created with the indecisiveness of the defenders.

Every coach in Super League will have looked at tapes of Wigan & will know exactly what Wigan are going to do. Every game I go to I see exactly the same structures of attack every week. The problem for the opposition and the reason we're so successful is that it is very, very, very difficult to stop. Our players are well drilled & know exactly where to be on every play. We have world class/top class players in key positions - Sam Tomkins/Brett Finch/Thomas Leuluai/Mike McIlorum/Sean O'Loughlin - which means our execution is top draw. Coupled with the fact these lads have had two years under Michael Maguire in which to improve/adapt to these plays means Wigan RL 2012 are very hard to stop.

In Attack
Towering Bombs with a good chase, if he drops them (or does not even attempt to catch them) you are a good chance to get the ball back. If he takes the catch clean him up in the tackle.

In defence
He has tended to crab across the ground at Test level looking for a defender to come out of the line, a sound defensive structure will limit those chances substantially.

I've only seen him play a couple of times, but what Jonesy said.

Go low, forget wrapping the ball up, let him get rid of it and hope your structures are good enough to get the next man in he line.

I'm sure they're as good as you say they are. And yet Tomkins (and Wigan) struggled to beat Fev. Fev wrapped him up and stopped him playing. He even knocked on in front of his own posts - had the referee awarded Fev the scrum instead of awarding Wigan a bizarre penalty on the next play the outcome could have been different ( stress on "could")
Wigan are good - how good does that make Fev?